Field of the Invention
The invention relates to a rotating assembly for a turbomachine, such as, more particularly, a turbojet engine in a plane, as well as a turbomachine comprising such an assembly.
Discussion of the Background
Such an assembly, which can be found, in particular, in a turbine, comprises a disc, and blades extending radially outwards from the disc and the feet of which are axially engaged and retained radially in of the recesses of the external periphery of the disc, said recesses alternating with teeth of the disc. The blades also comprise internal platforms arranged end to end on the circumference, so as to define together the internal limit of the flow of hot gas circulating in the turbine. The portion of the blade located inside relative to the jet, i.e. between the internal platform and the root, is called a tang. According to such positioning, spaces are formed between two adjacent tangs, and form inter-tang or inter-blade cavities. So-called recess bottom cavities are also formed by radial spaces located between the blade roots and the bottoms of the recesses.
In order to improve the performances of the turbomachine, and to prevent any heating of the disc by the flow of hot gas leaving the upstream combustion chamber and flowing through the jet, it is important to limit at most the circulation of such gas under the platforms and through the inter-blade cavities, using sealing means. As a matter of fact, the portion of the jet gas flowing under the platforms does not participate in the driving into rotation of the blades and directly heats the teeth of the disc. It is particularly advantageous to arrange the sealing means downstream of the inter-blade cavities so as to enable a pressurisation of such cavities to a value substantially identical with the one of the jet gas, which limits the suction effect in the cavities.
In the prior technique, for example in U.S. Pat. No. 4,507,052, a rotating assembly is provided for a turbomachine, comprising:                a disc having an external periphery having alternating recesses and teeth,        blades extending radially from the disc and the roots of which are engaged axially and retained radially in the recesses of the disc,        platforms extending circumferentially from the blades and which are arranged circumferentially end to end, with respect to each other,        axial sealing means for an upstream and/or downstream sealing of an annular zone extending radially between the platforms and the disc, said sealing means radially comprising an internal annular portion and an external annular portion structurally distinct from each other.        
Problems however exist, which concern sealing and efforts applied onto some moving parts (platform, disc . . . ), when the turbomachine is operating.
Additionally, when the blades are made of Ceramic Matrix Composite (in the following referred to as C.M.C.), the platforms also made of C.M.C. are even less able to bear the weight of the rotating trim strip, with the density ratio between a metallic material and a C.M.C. material ranging from three to four. Besides, as the dilatation ratio with an increased temperature ranges from two to three, the differential dilatations in operation between the trim strip on the one hand, and the blades and the disc on the other hand, may either enhance the constraints generated on the platforms, or create clearance enabling the circulation of the jet gas at the radial ends of the trim strip.